1. Field of the Invention
The present invention relates to the field of well pumps, and more particularly to a hydraulically operated portable pump jack for driving a reciprocating pump.
2. Brief Description of the Related Art
Conventional donkey head pump jacks have been in use for many years and typically include a walking beam pivotally movable supported by a Samson post with a first end of the walking beam having a donkey head thereon. A wire rope or cable assembly—bridle—connects the donkey head to the upper end of a sucker rod for reciprocating the sucker rod and the down hole pump mounted thereto. The walking beam is driven—at a second end opposite to the first end—by pitman arms which in turn are connected to eccentric cranks on a crank shaft with respective counterweights.
Unfortunately, such pump jacks require substantial maintenance in order to retain the movable components—with the walking beam, the donkey head, and the counter weight being very heavy—properly adjusted and operating. Furthermore, due to the heavy weight of the walking beam, the donkey head, and the counter weight, large forces are acting on the components of the pump jack resulting in substantial wear and material fatigue.
Another disadvantage of the conventional donkey head pump jacks is the need for proper support due to the heavy moving components. Typically, the conventional pump jacks are mounted with bolts to concrete pads which are supported using driven or screw in pilings in the ground making it expensive and time consuming to install, especially in remote areas. Moreover, the heavy movable components and heavy frame components as well as the concrete pads make transportation of the conventional pump jacks extremely time consuming and expensive.
Another disadvantage of the conventional pump jacks is the substantial safety hazard posed by the belt drives, the large rotating counter weights, the pitman arms, and the pivoting walking beam with the donkey head.
Another type of pump jacks are hydraulic pump jacks comprising a substantially vertically oriented hydraulic cylinder which is directly mounted to the well head. The piston of the hydraulic cylinder is directly connected to the sucker rod for providing the reciprocating action acting thereon. The hydraulic pressure for providing the reciprocating action is typically provided by a hydraulic pump driven by a small block gas engine.
While the hydraulic pump jacks are light in construction they still require a crane for installation. Furthermore, they are limited for use with only shallow wells. The side mounting of the hydraulic cylinder on the well head together with the direct mounting of the piston to the sucker rod causes side loading on the hydraulic cylinder, prematurely tearing seals and packing in the gland of the hydraulic cylinder. The resulting oil leaks require regular repair and oil spill attention. Usually, the small block gas engine runs on full power to push the sucker rod up and idles down to lower the sucker rod. The frequent changes from full power to idling and vice versa cause damages to the engine and substantially increases fuel consumption. The complicated electronic direction control of the reciprocating action frequently causes problems, especially in cold conditions.
It is desirable to provide a pump jack that is easy to transport and install.
It is also desirable to provide a pump jack that has substantially reduced maintenance requirements.
It is also desirable to provide a pump jack that has substantially increased safety during operation.